WASHINGTON – When President Obama announced his new strategy in March for dealing with the problems of Afghanistan and Pakistan, he declared that America’s once-grandiose goals in the region should be narrowed to taking aim at Al Qaeda. To get the job done, he was already sending upwards of 21,000 more troops to Afghanistan, and he promised to pour billions of dollars in aid into development programs in the region.

There was only one hitch: Al Qaeda doesn’t really live in Afghanistan. It survives largely over the border in Pakistan, where American boots on the ground will never be tolerated. “This is the logical flaw in an otherwise pretty sophisticated plan,” one of the participants in the White House debate said at the time. “We have to stabilize Afghanistan. But if the goal is to take out Al Qaeda and its friends, we’re putting our troops in the wrong country.”

But only five weeks later, what seemed like a fissure in the plan – a fissure Mr. Obama himself discussed and fully understood, his aides say – has opened into a canyon. As Mr. Obama prepares to meet at the White House on Wednesday with President Asif Ali Zardari of Pakistan and President Hamid Karzai of Afghanistan, the agenda has been overwhelmed by the drive that insurgents inside Pakistan are mounting for control of swaths of the country.

The original intention for the meeting was to find ways to accomplish something the Pakistanis and the Afghans have never been able to engineer, no matter how hard Washington has pushed them to: A coordinated military effort to squeeze the Taliban and other insurgents on both sides of their long, wild border. Suddenly, that seems like the lesser of two urgent problems.

“The possibility is now real that we will see a jihadist state emerge in Pakistan – not an inevitable outcome, not even the most likely, but a real possibility,” said Bruce Riedel, the Brookings Institution scholar who served as the co-author of Mr. Obama’s review.

“And that is the real strategic nightmare for the United States,” he added.

Important as Afghanistan is to the United States, he said, the events of the past few weeks focused American minds on Pakistan’s uniquely toxic cocktail.

“It’s where the far greater strategic risks lie,” said Mr. Riedel, a former intelligence officer who has long navigated the dangerous currents of South Asia. “It has more terrorists per square mile than anyplace else on earth, and it has a nuclear weapons program that is growing faster than anyplace else on earth.”

Or, as Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, put it on Monday, “this isn’t about â€˜can do’ any more; this is about â€˜must do.’ ”

So in the land of no good options, what are some of the possibilities that Mr. Obama can explore? What can he accomplish sitting down with a weak Pakistani leader who spent years dodging charges of corruption, and whose early support in Washington has quickly soured? Or with an even weaker Afghan leader who was once a favorite of the United States – both for his elegance and for his eloquence – but who many the Obama administration would now like to see eased out of office in the coming election?

Here are a few possibilities to watch for:

Speed Up Plan A The core of Mr. Obama’s strategy was to bet on a long-term solution: Retraining the Pakistani military to become an effective counterinsurgency force and pour billions of dollars and plenty of manpower into real nation-building efforts on both sides of the border, but particularly in the tribal areas that have become Al Qaeda and Taliban strongholds – in short, to execute the Marshall Plan for the region that President George W. Bush first talked about in March 2002 but never executed.

According to administration officials, Mr. Obama is expected to promise to unlock nearly $1 billion in aid that the United States has promised but not yet delivered, and to announce a new training program for Pakistani soldiers, probably located in Kuwait so that American trainers need not set foot on Pakistani soil. But building schools and training soldiers takes time. And with the Taliban expansion threatening the country’s main East-West highway – the highway that leads to Islamabad – it is not clear that the long-term approach will address the immediate military emergency.

Step up Predator Attacks and Covert Ground Action Last summer Mr. Bush approved a covert plan allowing United States forces, for the first time, to use remotely piloted aircraft to attack not only Al Qaeda sites, but other insurgents that threaten either Afghanistan or Pakistan. President Obama continued that policy, but every proposed strike by the Predator drones has posed a awful choice: How do you blow up a house that has suspected terrorists in the basement if it also has seven-year-olds and their mothers in the living room? The popular anger in Pakistan about the drones has reached a fever pitch.

Mr. Obama’s aides have debated inviting the Pakistanis to participate the C.I.A.’s Predator program, actively managing the missions rather just permitting them to be mounted from a not-so-secret base on Pakistani territory. But many in the administration are hesitant, because past joint operations with Pakistan’s military and intelligence services have rarely worked.

“The question is whether the Taliban’s boldness has scared the Pakistanis enough to realize that they need our help,” one national security official involved in the debate said. “We don’t know the answer to that.”

There is similar concern about sending American special forces on missions deeper into Pakisitan, for fear of the political reaction if they are discovered operating inside Pakistan’s borders. (One of Mr. Bush’s aides put this problem pithily last summer when he asked, “How do you invade an ally?”)

Make Nuclear Arms the No. 1 Concern: In public, the administration says that no matter what inroads the Taliban make in Pakistan, the country’s nuclear arsenal is secure. “The Pakistani leadership and in particular the military is very focused on this,” Admiral Mullen said on Monday.

But when not speaking on the record, intelligence and administration officials say they cannot rely on vague assurances that the weapons and the nuclear materials are locked down. They worry about a stream of intelligence suggesting sophisticated efforts by Al Qaeda and others to place their sympathizers inside the nuclear infrastructure. (Pakistani officials say they extensively screen the thousands of nuclear workers and weed out anyone suspect. But even in the United States, such programs have failed in the past.)

So some officials argue for extending the American program to help secure Pakistan’s nuclear weapons, pressing Pakistan to develop joint plans to evacuate those weapons if they came under threat. It is doubtful that the Pakistanis, who fear the United States has secret plans to seize the arsenal, would ever agree.

The bluntest statement of concern to date came a week ago from Secretary of State Hillary Rodham Clinton, in an interview with James Rosen of Fox News. “If the worst, the unthinkable, were to happen, and this advancing Taliban, encouraged and supported by Al Qaeda and other extremists, were to essentially topple the government for failure to beat them back, then they would have the keys to the nuclear arsenal of Pakistan,” she said.

“We can’t even contemplate that,” she added. “We cannot let this go on any further, which is why we’re pushing so hard for the Pakistanis to come together around a strategy to take their country back.”

PESHAWAR, Pakistan – President Obama is pouring more than 20,000 new troops into Afghanistan this year for a fighting season that the United States military has called a make-or-break test of the allied campaign in Afghanistan.

But if Taliban strategists have their way, those forces will face a stiff challenge, not least because of one distinct Taliban advantage: the border between Afghanistan and Pakistan barely exists for the Taliban, who are counting on the fact that American forces cannot reach them in their sanctuaries in Pakistan.

One Pakistani logistics tactician for the Taliban, a 28-year-old from the country’s tribal areas, in interviews with The New York Times, described a Taliban strategy that relied on free movement over the border and in and around Pakistan, ready recruitment of Pakistani men and sustained cooperation of sympathetic Afghan villagers.

His account provided a keyhole view of the opponent the Americans and their NATO allies are up against, as well as the workings and ambitions of the Taliban as they prepared to meet the influx of American troops.

It also illustrated how the Pakistani Taliban, an umbrella group of many brands of jihadist fighters backed by Al Qaeda, are spearheading wars on both sides of the border in what for them is a seamless conflict.

The tactician wears a thick but carefully shaped black beard and a well-trimmed shock of black hair, a look cultivated to allow him to move easily all over Pakistan. He spoke on the condition of anonymity for fear of retribution by his fellow Taliban members.

But on an array of issues, discussed over six months of interviews with The Times, he showed himself to be knowledgeable of Taliban activities, and the information he provided matched up consistently with that of other sources.

He was well informed – and unconcerned, he said – of the plans of the head of the United States Central Command, Gen. David H. Petraeus, to replicate in Afghanistan some of the techniques he had used in Iraq to stop the Sunni tribes from fighting the Americans.

“I know of the Petraeus experiment there,” he said. “But we know our Afghans. They will take the money from Petraeus, but they will not be on his side. There are so many people working with the Afghans and the Americans who are on their payroll, but they inform us, sell us weapons.”

He acknowledged that the Americans would have far superior forces and power this year, but was confident that the Taliban could turn this advantage on its head. “The Americans cannot take control of the villages,” he said. “In order to expel us they will have to resort to aerial bombing, and then they will have more civilian casualties.”

The one thing that impressed him were the missile strikes by drones – virtually the only American military presence felt inside Pakistan. “The drones are very effective,” he said, acknowledging that they had thinned the top leadership of Al Qaeda and the Taliban in the area. He said 29 of his friends had been killed in the strikes.

The drone attacks simply prompted Taliban fighters to spend more time in Afghanistan, or to move deeper into Pakistan, straddling both theaters of a widening conflict. The recruits were prepared to fight where they were needed, in either country, he said.

In the fighting now under way in Buner and Dir Districts, in the North-West Frontier Province of Pakistan, the Pakistani Taliban are taking on the Pakistani Army in a battle that is the most obvious front of a long-haul strategy to destabilize and take over a nuclear-armed Pakistan.

In Afghanistan, the Pakistani Taliban are directly singling out the United States and NATO forces by sending guerrillas to assist their Afghan Taliban allies in ousting the foreigners from Afghanistan.

While to the Taliban those conflicts are one fluid and sprawling war, the border between Afghanistan and Pakistan has long presented a firm barrier for the United States.

Although Pakistan is an official ally of the United States, the Pakistanis will not allow American troops to cross the border from Afghanistan. They will also not allow the troops to be present as a fighting force alongside the Pakistani military in the tribal areas that Al Qaeda and the Taliban use as a base.

The United States has helped Pakistan and Afghanistan recently open a series of joint posts to share intelligence and improve border monitoring. But those efforts are slight when compared with the demands of a 1,600-mile frontier of unforgiving terrain.

Despite years of demands by American and NATO commanders for Pakistan to control Taliban infiltration, the Taliban tactician said getting his fighters over the border was not a problem. The Pakistani paramilitary soldiers from the Frontier Corps who guard the border were too busy looking after their own survival, he said.

He has already begun moving 80 Taliban fighters in four groups stealthily into Afghanistan in the past month to meet the new American forces, he said.

The tactician says he embeds his men in what he described as friendly Afghan villages, where they will spend the next four to six months with the residents, who provide the weapons and succor for the missions against American and NATO soldiers.

In March, he made a reconnaissance trip by motorcycle to Paktika Province in Afghanistan from Wana, the main city in South Waziristan, in Pakistan’s tribal areas, to make sure the route was safe for his men. It was.

The main task for his first two groups of fighters will be to ambush convoys of NATO goods and soldiers on the Kandahar-Kabul highway, a major supply line for the allied war effort. “We want to inflict maximum trouble, to lower their morale, to destabilize,” he said.

His guerrillas, in their late teens to mid-20s, are handpicked for their endurance and commitment, he said. Some, like him, were trained by the Pakistani government as proxy fighters against India in Kashmir and have now joined the Qaeda and Taliban cause.

In a new twist, cameramen instructed to capture video of faltering American soldiers for propaganda DVDs are increasingly accompanying the guerrillas.

The tactician, a heavily built man who says he has put on weight in the past two years and is now too heavy and old to fight, said he was loyal to a commander named Mullah Mansoor.

In turn, Mr. Mansoor serves under the aegis of Siraj Haqqani, the son of a veteran Afghan mujahedeen leader, Jalaluddin Haqqani.

The tactician worked mostly from Wana, where he owns a small business and where, he acknowledged, the American drone strikes had disrupted life. The threat of the drones had ended the custom of gathering in groups of 10 to 20 men to discuss the issues of the day. “The gossip has finished,” he said.

The relationship between the Pakistani Taliban and Qaeda operatives, most of whom are Arabs, is respectful but distant, according to his descriptions.

The Arabs often go to the bazaar in Wana. But they bristle when asked questions, he said. “They never tell us their activities,” he said.

But the Taliban are willing providers for Al Qaeda. “When they need a suicide bomber, like blowing up a government building, we provide it,” he said.

There was respect for the scale of Al Qaeda’s ambitions. “They have a global agenda, they have a big design,” he said.

The Taliban goal was more narrow. “Capturing Afghanistan is not an Al Qaeda mission,” he said. “It’s a Taliban mission. We will be content in capturing Afghanistan and throwing the Americans out.”

The Pakistani Taliban will fight as long as it takes to defeat the Americans, he said. At the end of this fighting season, he said, “We will have a body count, and we will see who has broken whose back.”

President Hamid Karzai has arrived in Washington, D.C. for an official four-day visit to the United States of America. President Karzai is leading a delegation of senior Afghan officials including Foreign Minister Rangin Dadfar Spanta; Defense Minister Rahim Wardak; Interior Minister Hanif Atmar; National Security Adviser Dr. Zalmay Rassoul; Finance Minister Omar Zakhilwal; Commerce Minister Wahidullah Shahrani; Agriculture Minister Mohammad Asif Rahimi and Director of National Intelligence, Mr. Amerullah Saleh.

During the visit, President Karzai is scheduled to meet with President Barack Obama and other senior US officials to discuss strengthening Afghanistan-US relations; the situation in Afghanistan and the region; as well as the combat against terrorism.

President Karzai will also take part in a Trilateral Meeting with President Asif Ali Zardari and US Secretary of State, Hillary Rodham Clinton, for strengthening regional cooperation to address the challenges in Afghanistan and the region.

Moreover, President Karzai is scheduled to sign a Memorandum of Understanding with his Pakistani counterpart on Improving Trade and Accession Facilitation.

As part of the agenda, the Ministers of Foreign Affairs, Interior, Agriculture and Finance, and the Director of National Intelligence will participate in separate working group sessions with their Pakistani counterparts for strengthening cooperation in relevant areas. The working group sessions will be chaired by the respective US counterparts.